Method of making pistons



May 20, 1930. JARDINE 1,759,509

METHOD OF MAKING PISTONS Original Filed Sept. 25, 1926 INVENTOR PatentedMay 20, 1930 UNITED STATES PATENT OFFICE FRANK J'ARDINE, F CLEVELAND,OHIO, ASSIGNOR, BY MESNE ASSIGNMENTS, TO THE ALUMINUM COMPANY OFAMERICA, 0]? PITTSBURGH, PENNSYLVANIA A CORPORA- METHOD OF MAKINGPISTONS Original application filed September 23, 1926, Serial No.137,194. Divided and this application filed March Serial No. 262,641.

This invention relates to a method of making pistons and the like. It isparticularly adapted to the making of pistons composed of a plurality ofdifferent materials which have different co-eflicients of expansions andtend to produce great internal stresses in the pis- I tons when cast.

Pistons are frequently made of a plurality of different materials, asfor example, aluminum or aluminum alloy pistons, in which areincorporated steel or iron members for restraining or controlling theexpansion of the more expansible material. This type of piston isclaimed broadly in my co-pending application, Serial No. 47,214, filedJuly '31, 1925. A common way of forming such pistons is to cast the mainparts of the pistons about the control members so that these are 4 atleast partly imbedded withiii the remainder of the pistons. Upon coolingafter the casting operation the different materials tend to contract atdifferent rates and thus set up great internal stresses.

It is an object of this invention toprovide a method of eliminating fromsuch pistons some of the internal stresses normally set up therein andof relieving substantiallyall others.

The invention will be better understood from the description of onepractical embodiment thereof illustrated in the accompanying drawings,in which Fig. 1 is a side elevation of a finished piston made accordingto the invention.

Fig. 2 is a longitudinal section thereof taken on the line 22 of Fig. 1.

fig. 3 is a bottom plan View of the piston, an

ing the piston casting before machining.

The piston has a head consisting of'a top 1 and a depending annularflange 2 which maythe head are walls 4 which carry wrist pin Fig. 4 is aview similar to Fig. 1, but show- I v p I 2 by cored slots 19.'Thesecored: slots permit bosses 5 and 6 and are strengthened andstiffened by webs 7 and 8.

Below the piston head is a skirt comprising bearing or thrust faces 9and 10 which are joined beneath the wrist pin bosses by straplikeconnectors 11. Bearing face 9 is shown as integrally joined to walls 4by webs 12. The bearing faces are tied together and to the boss carryingwalls by control members A and I B, shown as hollow squares having theirends embedded in ridges 13 on the inside of the bearing faces, and theirsides spanning the space bet-ween the bearing faces, with theintermediate parts of the sides embedded in the boss carrying walls. Thecontrol members are of a material which will cause the, diameter of thepiston to change only as desired, for instance at the rate of change ofthe cylinder in which it operates.

, The connectors 11 are split at 14 and the splits spanned by arcuatebridges or culverts 15, the splits and culverts allowing for theperimetrical expansion of the skirt.

Bearing face 9 is shown joined to the piston head by a relatively narrowneck or web 16 while bearing face 10 is separated from the head by anair gap 17.

The piston is made as follows The control members A and B are placed ina mold and the balance of the piston cast around them. The differentcontraction of the various parts of the piston upon cooling, 1

'the'outeredges of the bearing or thrustjfaces to adjust themselvesindependently of the head "and so prevent the production of somestressesboth in the faces {and head.

After casting, one or both bearing faces After this heat treatment thepiston may be machined without tending to deform itself, thusconsiderably facilitating its manufacture.

This application is a division of my copendino application, Serial No.137,194, filed on or a out Sept. 23, 1926, which application containsclaims to the article shown in this present application.

While I have described one embodiment of my inventionewith someparticularity, I do not limit myself to the precise details shown, butclaim as my invention all variations and modifications thereof comingwithin the scope of the appended claims.

1. The process of making an insert piston which comprises casting thepiston about the inserts, separating at least one bearing face from thepiston head, heat treating at about- 300 F. for about 50 hours, and thenmachining the casting.

2. The process of relieving stresses in an insert piston which comprisesseparating one of the bearing faces of the piston skirt from the headand then maintainin the piston at a temperature of about 300 for about50 hours.

3. The process of making an insert piston which comprises casting apiston blank having the bearing faces of the skirt integrally connectedwith the piston head at their centers and spaced therefrom at theirsides by cored slots, separating one bearing face from the piston head,heat-treating at about 300 F. for about 50 hours, and then machining thecasting.

4. The process of making an insert piston which comprises casting apiston blank with the bearing faces of the skirt thereof integrallyconnected to the head at their centers and spaced therefrom at theirsides by cored Y slots, partially machining the blank, heattreating theblank at about 300 F. for about 50 hours, and then finishing themachining of the blank. I

5. The process of making an insert piston which comprises casting ablank with hearing faces joined at their centers to the head and spacedtherefrom at their sides by cored

